The present invention relates to ceramic materials and methods of making the same, and more particularly, in one representative and exemplary embodiment, to a high K, high Q (e.g., low loss) composition for reducing the sintering temperature of BZN compositions in multilayer LTCC (e.g., Low Temperature Cofired Ceramic) applications.
The use of green ceramic tapes has become popular in the manufacture of multilayer ceramic devices for routing electronic circuitry. For example, U.S. Pat. No. 5,801,108 discloses various engineering constraints typically encountered in the manufacture of such devices. Traditionally, many electronic components such as capacitors and resistors are surface mounted onto multilayer ceramic substrates. The processes typically involved in the fabrication of such circuitry can often be expensive, time consuming and/or labor intensive. Desirably, such devices may exhibit attractive values of xe2x80x9cQxe2x80x9dxe2x80x94a dimensionless metric that is inversely proportional to the efficiency factor of a given material (e.g., higher Q values generally correspond to lower loss).
One way to produce such multilayer ceramic packages involves the building-up of ceramic green tape layers using a paste of a desired material, such as a suitably adapted particulate material suspended in a binder. Upon processing, the binder may be effectively eliminated with the residual particulates of the desired material thereafter sintered to generally form a more densified structure.
Bi2O3xe2x80x94ZnOxe2x80x94Nb2O5 typically demonstrates unique dielectric properties. Between about 1-5 GHz, the cubic phase (Bi0.5Zn0.5)(Zn0.5Nb1.5)O7 generally has a dielectric constant on the order of about K=140 with a temperature coefficient of capacitance of around Tc=xe2x88x92400 ppm/xc2x0 C. The pseudo-orthorhombic phase Bi2(Zn1/3Nb1/3)2O7 generally has a dielectric constant of about K=80 and a temperature coefficient of capacitance of about Tc=+200 ppm/xc2x0 C. Accordingly, a mixture of the two phases at a proper ratio may be exploited to produce relatively low Tc dielectric compositions. Typical ranges that have been previously characterized are between about 30-40 wt % cubic (Bi0.5Zn0.5)(Zn0.5Nb1.5)O7 phase and between about 60-70 wt % pseudo-orthorhombic Bi2(Zn1/3Nb1/3)2O7 phase; this mixture hereafter referred to as xe2x80x9cBZNxe2x80x9d. Dielectrics within this composition range typically have K on the order of about 90-95 with Q values greater than or equal to about 500 as measured in the 0.5-1.0 GHz frequency band. However, the sintering temperature of such dielectrics is typically on the order of 950-1050xc2x0 C. xe2x80x94generally much higher than the desired sintering temperature for most Low Temperature Cofired Ceramics (LTCC).
There is a need for improved cofireable dielectric compositions for making BZN-based devices; preferably materials that have relatively flexible processing characteristics and exhibit an attractive dielectric constant (e.g., K) and Q value. Specifically, there exists a need to provide a dielectric composition and method of making such materials and multilayer substrates that demonstrates the characteristics necessary for economical use in, for example, RF device applications while avoiding the processing limitations otherwise inherent in the prior art. Moreover, the material should be easily and reproducibly fabricated or otherwise amenable to manufacturing methods that produce device packages with consistent electrical and/or mechanical properties. Accordingly, despite the best efforts of the prior art, there is a need for improved dielectric compositions for effectively reducing the sintering temperature of BZN.
In various representative aspects, the present invention provides a composition of matter and method of using a glass sintering aid to reduce the sintering temperature of BZN. A representative application of the disclosed technology provides high K, low loss cofireable dielectric compositions for the manufacture of embedded capacitors in LTCC packages.
Additional advantages of the present invention will be set forth in the Detailed Description which follows and may be obvious from the Detailed Description or may be learned by practice of exemplary embodiments of the invention. Still other advantages of the invention may be realized by means of any of the instrumentalities, methods, compositions or combinations particularly pointed out in the Claims.